The present invention relates to an improved composition based on a polypropylene homopolymer and/or copolymer for manufacturing and/or producing caps for carbonated drinks having enhanced properties of rigidity and leak-tightness without the need for using additional seals made of poly(ethylene-vinyl acetate) (EVA) polymers or other polymers such as polyethylene polymers and to the method for the manufacture thereof, in particular for the use thereof in the industry of carbonated drinks and soft drinks and/or with any type of container that requires a cap.
Currently, caps without seal made of polypropylene or polyethylene are used only for capping bottles for water with satisfactory results given that they have no leaks; however, these types of caps without polypropylene and/or polyethylene type seal (liner) cannot be used with carbonated products due to the carbon dioxide gas that has been added to the soft drinks; this is because the cap does not resist the pressure of the pressurized liquid inside the vessel; in order to solve this problem, the improved composition according to the invention includes: a polypropylene homopolymer and/or copolymer; an ethylene-octene and/or ethylene-methyl acrylate elastomer, and an additive selected from a lubricating or sliding agent, a nucleation agent, an antioxidant, an antistatic agent and/or a mixture of same; it provides the flexibility necessary to give the cap the softness, rigidity (strength) and leak-tightness so that the pressure does not overcome the cap causing the loss of carbon dioxide gas that has been added to the sodas.
Currently, polyethylene and polypropylene caps are also known that are provided with a type of seal (liner) for capping bottles of carbonated drinks and/or sodas; however, the associated process is more expensive, since it involves the use of two materials, one for the cap and the other for the seal, in addition to integrating the seal with the cap. This represents a problem as it increases the production costs.
Polyethylene caps are also known that do not have a type of seal (liner) for capping bottles of carbonated drinks and/or sodas; however, to prevent leaks, the design of the shape of the internal flange of the cap and the cap itself had to be greatly changed; satisfactory results have been obtained with this modification in preventing leaks, but unfortunately the production time for each one the caps has increased; as it is, the improved composition of the present invention solves this problem as well, as it results in the obtention of caps without seals and is associated with an increase in the production thereof.
The improved composition of the present invention also solves this problem as it results in the obtention of caps without seals. The seals that have already been used are of the poly(ethylene-vinyl acetate) (EVA) type (liner); upon elimination of the seal from the caps, the caps now are cleaner since they are made of a single material.
The document KR20130034119 (Abstract) describes a PAC type medical container with draw off ring (cap) for reducing the product defects and for facilitating the use by maintaining the openability with less change in the force it takes to open it after high-temperature sterilization. The cap-type ring is manufactured according to the following process steps: —injection molding of 40-60% by weight of polypropylene and 40-60% by weight of elastomer, and sterilization at 121 degrees Celsius or higher. It has a percentage of change (%) of the openability before and after the sterilization process that satisfies the following equation 1: Os1=openability of the cap before the sterilization process (kgf). Os2=openability of the cap after the sterilization process (kgf). However, this composition is different from the composition of the present invention, and in addition, the product obtained (cap) has different properties of use, and as a result it is not detrimental to novelty or inventive step.
The document CN102453279 (Abstract) relates to a polypropylene composition for the production of a bottle cap for a carbonated drink. The composition includes the following substances: 30-60 parts of a polypropylene homopolymer with an isotacticity greater than 99% and a MFR of 1-30 g/10 min; 30-60 parts of the block of a polypropylene copolymer with a MFR of 1-15 g/10 min; 4-20 parts of polyethylene with a density of 0.955-0.968 g/cm3 and a MFR of 1-15 g/10 min; 5-15 parts of polyolefin elastomer; 0.05-0.2 parts of nucleation agent, and 0.3 to 1 part of sliding agent. The product has excellent rigidity and a satisfactory resistance to impact and stress. However, this composition is different from the composition of the present invention, since the percentages of each one of the components are different and, in addition, it includes 4-20 parts of polyethylene with a density of 0.955-0.968 g/cm3 and a MFR of 1-15 g/10 min; this document also mentions that if all the components are not in the composition, the resulting product has unsatisfactory properties (comparative Examples 1, 2 and 3); the product obtained (cap) using this composition has different properties of use from the cap of the present invention, and as a result it is not detrimental to novelty or inventive step.
The document CN101792558 refers to an internal cap material for transfusion bags and to a method for preparing and applications of same. The preparation method includes the following steps: uniformly mixing 30-70 parts of polypropylene, 0-30 parts of polyethylene, 10-40 parts of elastomer, 2-8 parts of flow modifier and 0.5-2 parts of antioxidant, adding while mixing in an extruder at 130-180° C. at the speed of 30-70 rpm; extrusion at the speed of 200-500 rpm; cooling with water, drying, granulation so as to obtain the internal cap material for transfusion bags, wherein the melting index of the internal cap material at 190° C. and under the pressure of 2016 g is 5-15 g/10 min. The internal cap material has the advantage of high tenacity and a satisfactory radiation tolerance. The internal cap material for transfusion bags can be processed by injection molding directly for preparing the internal stoppers for transfusion bags. The yellowing index of the internal cap subjected to radiation with respect to 25 kg using gamma rays is less than or equal to 10, and the rate of rupture of the transfusion cap kit after perforation with a transfusion contact pin can be less than or equal to 2%. However, this composition is different from the composition of the present invention, since the percentages of each one of the components are different, and in addition the product obtained has different properties of use, and as a result it is not detrimental to novelty or inventive step.
The document JP2010222032 relates to a cap lining, which allows retort processing and is characterized by gas barrier properties, sealing capacity or similar properties, and is used to produce a cap and a capped bottle. The liner of the cap 5 provided within the cap 1 and the seal of the mouth of the bottle are formed by polypropylene resin and the hydrogenation of rubber made of a conjugated diene styrene block copolymer, that is to say a polystyrene elastomer obtained by kneading styrene styrene-ethylene-butylene or ethylene styrene-propylene styrene with a MFR of 0.01 g/10 min (200 [degree] C. 5 kg) or lower and polybutene with a viscosity of 40-280 mm2/S at 100° C. The cap lining contains 10 to 65% by weight of polybutene. However, this composition is different from the composition of the present invention, since the percentages of each one of the components are different, and in addition the product obtained has different properties of use, and as a result it is not detrimental to novelty or inventive step.
The document JP2008019003 relates to a polypropylene stopper that does not result in whitening including when the cap is made from a colored polypropylene that includes a dye (except for white), and having performances including moldability, workability, opening pluggability, resistance to impact, or similar properties. The polypropylene stopper is made from a resin composition which includes 70-95% by weight of a homopolypropylene and 5 to 30% by weight of a modifier consisting of a polyolefin-based elastomer and has a bending modulus of 800 to 2000. However, this composition is different from the composition of the present invention, since the percentages of each one of the components are different, and in addition the product obtained has different properties of use, and as a result it is not detrimental to novelty or inventive step.
The document MX2007010929 relates to vulcanized thermoplastics cured with peroxide, which include a thermoplastic (polypropylene) and an isomonoolefin-multiolefin elastomer such as butylene rubber. More particularly, the invention relates to vulcanized thermoplastics cured with peroxide, in which the elastomer includes at least 3.5 mol % of a multiolefin for the purpose of facilitating the curing with peroxide. The vulcanized thermoplastics according to the present invention are useful in the preparation of molded articles for applications requiring high purity, such as condensor caps, medical components and fuel cell components. However, this composition is different from the composition of the present invention, since the percentages of each one of the components are different, and in addition the product obtained has different properties of use, and as a result it is not detrimental to novelty or inventive step.